Search results for "Hamiltonian"
showing 10 items of 662 documents
Entanglement dynamics in a spin star system
2009
The implementation of more and more efficient nanodevices exploitable in applicative contexts like for example quantum computers often requires a highly challenging miniaturizing process aimed at packing a huge number of point-like basic elements whose dynamics mimics indeed that of a qubit. Stimulated by such a requirement, over the last few years theoretical schemes using the language of the spin ½ system models have been investigated. The main reason is that besides the simple dynamical behaviour of each elementary constituent these Hamiltonian models do indeed capture basic ingredients of several physical situations differing one another mainly for the numerical values of some relevant …
The bound state in the spectrum of the Lee–Friedrichs Hamiltonian
2000
Abstract The spectrum of the Lee–Friedrichs Hamiltonian, describing a two-level system embedded in a continuum, is considered. An appropriate discretization of the field modes is performed before taking the continuum limit. It is shown that the existence of an eigenstate with negative energy (bound state) is related to the nonanalyticity of the Friedrichs spectral representation. This negative energy state is a dressed state and its physical properties are studied in some significant cases.
Exchange Interactions II: Spin Hamiltonians
1996
In Part I the physical mechanism of exchange interactions have been discussed. In this part we introduce the general concept of spin-hamiltonian. Isotropic exchange hamiltonian for many-electron polynuclear clusters (Heisenberg-Dirac-van Vleck-HDVV model [1-6]) will be derived. Spin-hamiltonian approach allows to separate the full exchange problem into two independent ones: 1) evaluation of the energy levels of the exchange system considering Jij as a set of semiempirical parameters, and 2) quantum mechanical calculation of exchange parameters with the aim of elucidation of the main physical mechanisms of the exchange coupling. In this part we shall focus on the problem of calculation of sp…
Electronic structure of a quantum ring in a lateral electric field
2001
The electronic states of novel semiconductor quantum rings (QR's) under applied lateral electric fields are theoretically investigated for different values of the ratio ${r}_{2}{/r}_{1},$ where ${r}_{2}$ ${(r}_{1})$ is the outer (inner) radius of the ring. The eigenstates and eigenvalues of the Hamiltonian are obtained from a direct matrix diagonalization scheme. Numerical calculations are performed for a hard-wall confinement potential and the electronic states are obtained as a function of the electric field and the ratio ${r}_{2}{/r}_{1}.$ An anomalous behavior in the energy vs. electric-field fan plot due to the break of symmetry is predicted. Analytical expressions for the energy level…
Sine-Gordon Statistical Mechanics
1984
The Classical partition-function $$ Z = \int {D\Pi {\text{ }}D\phi {\text{ }}\exp - } \beta H\left[ \phi \right]$$ (1) in which \( {\beta ^{{ - 1}}} = {k_{B}}T{\text{ and }}H\left[ \phi \right]\) is the sine-Gordon (s-G) Hamiltonian $$ H\left[ \phi \right] = {\Upsilon _{0}}^{{ - 1}}\int {\left[ {\frac{1}{2}{\Upsilon _{0}}^{2}{\Pi ^{2}} + \frac{1}{2}{\phi _{z}}^{2} + {m^{2}}\left( {1 - \cos \phi } \right)} \right]} dz $$ (2) has been evaluated by transfer integral methods [1,2].
Fourier-transform spectroscopy and coupled-channels deperturbation treatment of theA 1Σ+–b 3Πcomplex of KCs
2010
The laser-induced fluorescence (LIF) A {sup 1{Sigma}+}-b {sup 3{Pi}{yields}}X {sup 1{Sigma}+} spectra of the KCs molecule were recorded in a near infrared region by a Fourier-transform spectrometer with a resolution of 0.03 cm{sup -1}. Overall more than 200 collisionally enhanced LIF spectra were rotationally assigned to {sup 39}K{sup 133}Cs and {sup 41}K{sup 133}Cs isotopomers yielding more than 3400 rovibronic term values of the strongly mixed singlet A {sup 1{Sigma}+} and triplet b {sup 3{Pi}} states with the uncertainty of 0.003-0.01 cm{sup -1}. Experimental data massive starts from the lowest vibrational level v{sub A}=0 of the singlet and nonuniformly covers the energy range E is an e…
Detuning-induced robustness of a three-state Landau-Zener model against dissipation
2019
A three-state system subjected to a time-dependent Hamiltonian whose bare energies undergo one or more crossings, depending on the relevant parameters, is considered, also taking into account the role of dissipation in the adiabatic following of the Hamiltonian eigenstates. Depending on the fact that the bare energies are equidistant or not, the relevant population transfer turns out to be very sensitive to the environmental interaction or relatively robust. The physical mechanisms on the basis of this behavior are discussed in detail.
New physics vs new paradigms: distinguishing CPT violation from NSI
2019
Our way of describing Nature is based on local relativistic quantum field theories, and then CPT symmetry, a natural consequence of Lorentz invariance, locality and hermiticity of the Hamiltonian, is one of the few if not the only prediction that all of them share. Therefore, testing CPT invariance does not test a particular model but the whole paradigm. Current and future long baseline experiments will assess the status of CPT in the neutrino sector at an unprecedented level and thus its distinction from similar experimental signatures arising from non-standard interactions is imperative. Whether the whole paradigm is at stake or just the standard model of neutrinos crucially depends on th…
Quantum Monte-Carlo calculation of correlation functions of undistorted, cis-distorted and trans-distorted polyacene
2003
Abstract We have studied polyacene within the Hubbard model to explore the effect of electrons correlations on the bond–bond correlation as well as spin–spin correlation functions. We employ the determinantal quantum Monte-Carlo to resolve the microscopic Hamiltonian of this system which involves a nearest-neighbor electron hopping matrix element t , an on-site Coulomb repulsion U . The objective of this study is to understand the effect of electron–electron (e–e) correlations on the structural instability in polyacene. We find strong similarities between polyacene and polyacetylene. The system shows no tendency to destroy the imposed bond-alternation pattern. The spin–spin correlations sho…
Infinite orbit depth and length of Melnikov functions
2019
Abstract In this paper we study polynomial Hamiltonian systems d F = 0 in the plane and their small perturbations: d F + ϵ ω = 0 . The first nonzero Melnikov function M μ = M μ ( F , γ , ω ) of the Poincare map along a loop γ of d F = 0 is given by an iterated integral [3] . In [7] , we bounded the length of the iterated integral M μ by a geometric number k = k ( F , γ ) which we call orbit depth. We conjectured that the bound is optimal. Here, we give a simple example of a Hamiltonian system F and its orbit γ having infinite orbit depth. If our conjecture is true, for this example there should exist deformations d F + ϵ ω with arbitrary high length first nonzero Melnikov function M μ along…